1. Field of the Invention
The present invention relates to a coupling apparatus for connecting a braking input element to a brake master cylinder of a vehicle, and to a method for operating a coupling apparatus of this kind.
2. Description of the Related Art
Electric and hybrid vehicles have a braking system designed for regenerative braking, having an electric motor operated in generator mode in the context of regenerative braking. The electrical energy recovered upon regenerative braking is preferably used, after temporary storage, to accelerate the vehicle. It is thereby possible to reduce a power dissipation exhibited by a conventional vehicle when frequently braking during a journey, as well as the energy consumption and pollutant emissions of the electric or hybrid vehicle.
Operation of the electric motor, for example the electric drive motor, in generator mode usually requires, however, a specific minimum vehicle speed. A regenerative braking system is thus frequently incapable of exerting a generator-mode braking torque on the wheels of the vehicle for a long enough time for the forward-traveling vehicle to be at a standstill. A hybrid vehicle therefore often also has, in addition to the regeneratively operated electric motor, a hydraulic braking system with which the absent braking effect of the regenerative brake can be compensated for at least in a low-speed range. In this case even if an electrical energy reservoir is full, a circumstance in which the regenerative brake usually does not exert a braking torque on the wheels, the entire braking torque can be applied via the hydraulic braking system.
On the other hand, it is desirable in many situations to exert the least possible hydraulic braking force on the wheels in order to achieve a high degree of regeneration. After shifting operations, for example, the decoupled generator is often activated as a regenerative brake in order to ensure reliable charging of the temporary reservoir and a high level of energy savings.
A driver generally prefers a total braking torque for his or her vehicle that corresponds to his or her actuation of a braking input element, for example his or her actuation of the brake pedal, irrespective of activation or deactivation of the regenerative brake. Many electric and hybrid vehicles therefore have an automatic system that is intended to adapt the braking torque of the hydraulic braking system to the current braking torque of the regenerative brake in such a way that a desired total braking torque is maintained. The driver him- or herself therefore need not take on the task of the deceleration controller by adapting the actuation of the braking input element to the current braking torque of the regenerative brake. Examples of an automatic system of this kind are brake-by-wire braking systems, in particular EHB systems, such as those described e.g. at http://en.wikipedia.org/wiki/Brake-by-wire.